The versatility and flexibility of industrial robots has increased significantly as a result of the development in the field of computer technology. A robot may be used for very different types of industrial tasks, including spot-welding components of a car as well as tasks that are commonly called pick and place. Pick and place tasks include picking up objects from a conveyor belt and placing them on a shipping pallet or in a shipping carton. A well known example is that of picking up chocolates from a conveyor belt, and placing them in a packing tray or a chocolate box.
A typical pick and place system comprises an input conveyor on which items are conveyed from an item source. The items are conveyed to a pick and place robot that picks the items up and places them on an output conveyor. The flow of items on the input conveyor, i.e. the number of items being conveyed per unit time, may vary to a small or great extent. Similarly, the ability for the output conveyor to receive items may also vary. For example, if the output conveyor slows down or even stops during a shorter or longer duration, it may become impossible for the pick and place robot to place items due to the fact that the output conveyor is already full of placed items within the placing range of the robot.
Such variations regarding item flow and availability of placing positions is a problem that needs proper attention when designing a pick and place system, in particular the way in which a pick and place robot is to operate in the system.
Needless to say, this problem is even more complex when the pick and place system comprises a plurality of output conveyors and a plurality of pick and place robots.
Prior art patent application published as US 2007/0108109 describes a control method for machines in a pick and place system. It describes a system involving a plurality of robots controlled by a master process where information from a sensor about positions of items on an input conveyor is used to distribute pick and place tasks between the robots.